We have previously described touch sensing systems employing a plane or sheet of light, for example as shown in FIGS. 1 and 2. These techniques may be employed for detecting touches or proximate to a surface.
FIG. 1 shows an example touch sensitive image projection device 100 comprising an image projection module 200 and a touch sensing system 250, 258, 260 in a housing 102. A proximity sensor 104 may be employed to selectively power-up the device on detection of proximity of a user to the device. The image projection module 200 is configured to project downwards and outwards onto a flat surface such as a tabletop; boundaries of the light forming the displayed image 150 are indicated by lines 150a, b. The touch sensing system 250, 258, 260 comprises an infrared laser illumination system 250 configured to project a sheet of infrared light 256 just above the surface of the displayed image 150 (for example ˜1 mm above, although in principle the displayed image could be distant from the touch sensing surface). The laser illumination system 250 may comprise an IR LED or laser 252, collimated then expanded in one direction by light sheet optics 254 such as a cylindrical lens. A CMOS imaging sensor (touch camera) 260 is provided with an IR-pass lens 258 and captures light scattered by touching the displayed image 150, with an object such as a finger, through the sheet of infrared light 256 (the boundaries of the CMOS imaging sensor field of view are indicated by lines 257, 257a, b). The touch camera 260 provides an output to touch detect signal processing circuitry as described further later. These techniques may be employed with any type of image projection system.
FIG. 2, this shows plan and side views of an example interactive whiteboard touch sensitive image display device 400 incorporating such a system. In the illustrated example there are three IR fan sources 402, 404, 406, each providing a respective light fan 402a, 404a, 406a spanning approximately 120° together defining a single, continuous sheet of light just above display area 410. The fans overlap on the display area (which is economical as shadowing is most likely in the central region of the display area). Typically such a display area 410 may be of order 1 m by 2 m. The side view of the system illustrates a combined projector 420 and touch image capture camera 422 either aligned side-by-side or sharing a portion of the projection optics. The optical path between the projector/camera and display area is folded by a mirror 424. In some cases, the sheet of light generated by fans 402a, 404a, 406a is close to the display area, for example less than 1 cm or 0.5 cm above the display area. However the camera and projector 422, 420 are supported on a support 450 and may project light from a distance of up to around 0.5 m from the display area.
There is, however, a desire for alternative/improved techniques. For example, in particular for large LCD display screens, it would be advantageous to be able to provide touch detection from a relatively low height above the display surface, for example less than 1 cm rather than by employing a camera looking down on the display surface. It is also desirable to reduce cost and improve the user experience, for example by improving the ‘refresh rate’ and reducing the noise.
One type of touch detection is described in US2009/0091553, in which a laser is raster scanned across a display from behind, beneath the display surface. Another typical scanning-type touch panel is described in US2001/0028344, employing a polygonal mirror to angularly scan laser light for touch detection. The system uses light scanned over the surface of a display screen and employs scanning angle/timing for touch detection but provides no distance information along the scanned beam, in a direction perpendicular to the sweep.
It is desirable to improve upon these known techniques.